The Yellow Jackets will face AC Flora 6:30 p.m. today on the road for the second game of the first round of the playoffs.
Chapin stung Union County in the second inning with two runs to take a 2-0 lead.
The Yellow Jackets came back in the top of the third inning when Daniel Revis scored on a throwing error, closing the gap 2-1.
Revis then lifted Union County with a three-run homerun in the top of the third inning plating Josh Simpson and Taylun Wallace for a brief 4-2 lead.
Chapin, however, answered in the bottom of the fourth inning scoring five runs off three Union County errors, taking a 7-4 lead.
Joe Beatty then scored on an error and Wallace had an RBI to plate Jarrod Cheek, closing the gap 7-6.
Union County then tied the game 7-7 when Simpson singled to allow Gerard Taylor to cross homeplate in the top of the sixth inning. Wallace then singled to plate Beatty, and Cheek and Simpson scored on a Chapin error to take a 10-7 lead.
Chapin answered right back scoring four runs of their own and taking a 11-10 lead for the win.
Union County (13-10 overall) must win tonight against AC Flora to stay in the playoffs. If they win, the Yellow Jackets will play again Monday.